1. Field of the Invention
This invention relates generally to medical device systems and, more particularly, to medical device systems and methods capable of assessing and managing epileptic events related to epilepsy based upon seizure classification.
2. Description of the Related Art
Generalized tonic-clonic status epilepticus, referred to herein as Convulsive Status Epilepticus (CSE), is a neurological emergency with an estimated incidence of about 20 out of 100,000 patients. CSE is also associated with a mortality rate between 3% and 40% depending on etiology, age, status type, and status duration and is considered in this disclosure an extreme event. CSE, in particular, requires immediate, aggressive, and effective treatment to stop seizure activity, to prevent neuronal damage, systemic complications, and the possibility of death. Most investigations on prognosis of status epilepticus (SE) have focused on mortality. Some research suggests that SE outcome basically depends on the etiological and biological background of the SE episode, and that the earlier the therapeutic intervention, the higher the probability of controlling it. Additionally, non-convulsive status epilepticus (nCSE), while not a medical emergency of the magnitude of CSE, is also an extreme epileptic event because it increases the risk of bodily injury and neurologic deficits such as permanent, potentially severe impairment of memory.
SE and CSE are defined based on the duration of a single seizure and its variations, or on the lack of recovery of certain neurologic functions to their inter-ictal (baseline) levels in the context of closely spaced seizures. While it is common to focus on seizure duration or frequency as measured from patient EEG, and whether the patient is conscious/aware or not, such a focus has important limitations, because signals or indices from other body systems (such as cardio-vascular, respiratory, endocrine, and metabolic) are adversely impacted by the seizures, undergoing extreme, life-threatening changes that do not receive the same attention as the seizures. These cardio-respiratory, metabolic, and endocrine extreme changes may directly contribute to the morbidity and mortality associated with SE. In the present state of the art, SE is viewed and treated narrowly (and ineffectively) as mainly a brain condition. Current diagnostic tools do not facilitate early detection/anticipation of extreme epileptic events, which may contribute to serious neurological and medical sequelae or even death associated with SE.
Sudden Unexpected Death in Epilepsy, or “SUDEP,” another extreme epileptic event, is a phenomenon in which a patient with epilepsy dies unexpectedly and without an apparent, outstanding cause—that is, the death is unexplained since autopsy results are unrevealing. One of the main risk factors for SUDEP is the lack of seizure control with first line drugs prescribed alone or in any safe combination and dosage. Whether or not the first in a chain of ultimately fatal events leading to SUDEP is a seizure, the defining event is likely to be either cardiac (e.g., ventricular fibrillation or asystole) or respiratory (e.g., apnea) or both. Currently, the monitoring, detection, prediction and prevention of SUDEP are inadequate and markedly limited in breadth and depth of scope, as demonstrated by the fact that such deaths are, by definition, unexpected.
SE and/or CSE alter autonomic nervous system function, and SUDEP may be caused by autonomic dysfunction. Brain/neurological activity, such as electrical activity, whether normal or abnormal, and autonomic functions (e.g., cardiovascular activity, respiration, etc.), referred to herein as body signals, are functionally tightly coupled, and monitoring these body signals may provide valuable information. SE and CSE also increase the risk of body injuries associated with seizures which may result from the impairment of the patient's consciousness or awareness. Injuries such as bone fractures and burns, for example, and adverse changes in body functions during a seizure, may increase the risk of mortality to the patient independent of the seizure itself. Such injuries may qualify a seizure as an extreme event regardless of its severity or closeness in time to a prior seizure (inter-seizure interval). On the other hand, certain seizure severity or inter-seizure interval values may suffice to classify a seizure as an extreme event irrespective of the impact on body functions/systems.